1. Field of the Invention
This invention relates to the control of pathogenic infections of fish, and more particularly to the administration of vaccines for such control.
2. Description of the Related Art
Infectious diseases are a major constraint to the expansion of aquaculture. The use of drugs and antibiotics in aquaculture is highly regulated in order to avoid risks to the public safety, to animal health, and to prevent the development of resistant strains of disease organisms. Consequently, the farmer is left with few resources like vaccination, early diagnosis, and good husbandry techniques.
DNA immunization constitutes a new and promising approach to vaccination. It consists in the introduction of a plasmid vector mediating expression of antigen/s into the tissue of an animal in order to elicit an immune response (Ulmer J B, Sadoff J C, Liu M A. DNA vaccines. Curr Opin Immunol 1996; 8:531-6). It has been shown that DNA immunization provides protection against infection by a variety of pathogens, including protection of rainbow trout against infection by infectious hematopoietic necrosis virus (Anderson E D, Mourich D V, Fahrenkrug S C, LaPatra S, Sheperd J, Leong Jo-AC. Mol Mar Biol Biotech 1996; 5:114-22), viral hemorrhagic septicemia (Lorenzen N, Lorenzen E, Einer-Jensen K, Heppell J, Wu T, Davis H. Fish Shellfish Immunol 1998; 8:261-270), and bacterial kidney disease (Gómez-Chiarri M, Brown L L, Levine R P. In: Aquaculture Biotechnology Symposium Proceedings. Physiology Section of the American Fisheries Society, 1996; 155-157). DNA immunization is especially attractive for the development of vaccines against diseases caused by virus, parasites, and intracellular pathogens, where T cells are the central mediators of protection and pathology.
Two major roadblocks to the licensing and commercialization of DNA vaccines for aquaculture are the availability of safe and efficacious expression vectors and economic and efficient methods of delivery. The Center for Biological Evaluation and Research (CBER) of the Food and Drug Administration (FDA) has released a draft of points to consider in designing DNA vaccines (See “Points to consider on plasmid DNA vaccines for preventive infectious disease indications” published December 1996 by the U.S. Food and Drug Administration Center for Biologics Evaluation and Research Office of Vaccine Research and Review). Of concern is the source of the DNA incorporated into the vector, including eukaryotic promoters and enhancers; termination/polyadenylation addition sites; antibiotic resistance markers; and other selection markers. In considering the use of an antibiotic resistance marker CBER is advising manufacturers against the use of penicillin or other β-lactam antibiotics. When an antibiotic resistance marker is required in a plasmid DNA vaccine construct, CBER advises the use of an antibiotic such as kanamycin or neomycin. These aminoglycoside antibiotics are not extensively used in the treatment of clinical infections due to their low activity spectrum, prevalence of kanamycin-resistant bacteria, and their problematic therapeutic index with toxicities including irreversible citotoxicity and nephrotoxicity. Furthermore, although the use of viral promoters and mammalian and viral termination and polyadenylation signals in the design of DNA vaccines is not a main consideration in the CBER draft, there is a general public concern on the use of viral and mammalian sequences in agricultural products.
Concerning the routes of administration, previous studies in the development of DNA vaccines for fish have used direct injection of naked DNA as a method of vaccine delivery into the fish. This method of DNA delivery is efficient and simple, but requires fish handling. Alternative methods for vaccine delivery that are simple and more economic include bath and immersion. However, the efficacy of the bath and immersion methods is reduced because the water and the skin and mucus of the fish are abundant in enzymes that can degrade DNA.
The present invention provides the tools for an effective and economic method for the delivery of DNA vaccines into finfish and other aquatic species.